Inhibitor acid



Patented Sept. 24, 1957 INHIBITOR ACID George S. Gardner, Elkins Park,and Albert J. Saukaitis, Wayne, Pa., assignors to American ChemicalPaint Company, Ambler, Pa., a corporation of Delaware No Drawing.Application December 2, 1953, Serial No. 395,852

2 Claims. (Cl. 252-448) This application is a continuation-in-part ofour earlier application, Serial Number 332,491, filed January 21, 1953,now abandoned.

The invention relates to inhibitors such as are useful in the art ofcontrolling the attack of acids on metals and is particularly concernedwith the provision of new and improved inhibitors and inhibitorformulations as well as to a method for producing the same.

Before reciting the objects of the invention we wish to point out thatorganic nitrogen bases, especially those that are derived from coal tar,are ofparticular value as inhibitors in acid pickling baths and thatvarious organic nitrogen compounds have been used in the pickling art.The compounds most widely used and of the most value at the present timeare the cyclic bases of the aromatic series such as pyridines,quinolines, acridines and certain of their derivatives. Other nitrogenring compounds of value as inhibitors are such as those disclosed inUnited States Patent No. 2,010,562. Unfortunately, however, the supply,quality and uniformity of naturally occurring bases suitable for themanufacture of pickling inhibitors have always been variable and theindustry has long felt a need for a source of supply based upon easilyobtainable chemicals from which pickling inhibitors of the type referredto can be produced. The present invention makes this possible and at thesame time provides new inhibitors and inhibitor formulations which aremarkedly improved both as to strength and as to useful length of life inthe acid solutions in which they are employed.

With the foregoing in mind, the principal objects of the invention maybe recited as residing in the provision of new inhibitors of greatlyincreased inhibiting power and of exceptionally long life, the provisionof a simple and effective method for the production of such inhibitors,which method makes use of relatively inexpensive and readily availableraw materials and, finally, the provision of inhibitors and a method ofproducing the same, which are capable of far more exact control than hasheretofore been possible so that quality and uniformity are very muchimproved. 7

By way of background, it should be noted that Mannich and his co-workershave shown that it is possible to prepare piperidine derivatives bymeans of a modification of the reaction now known as the Mannichreaction. If one molecule of methylamine hydrochloride reacts with twomolecules of formaldehyde and two molecules of acetone, a compound isobtained having the following structural formula:

No. l

O CH:

By making the reaction product alkaline in the cold, a condensationtakes place, and a piperidine derivative is formed having the followingstructural formula:

wherein R is alkyl, arylalkyl, cyclo-alkyl, hydrogen or the group and R1is alkyl, aryl, or aryl-alkyl. Typical examples of R are methyl, ethyl,isopropyl, n-propyl, n-butyl, nhexyl, n-octyl, benzyl, alpha naphthylmethyl, cyclohexyl and cyclopentyl. Suitable examples of R1 are methyl,ethyl, n-propyl, n-amyl, isobutyl, phenyl, naphthyl, benzyl, and alphanaphthyl methyl.

The present invention is based upon the discovery that the substitutedpiperidines of No. 3 and certain of their derivative are excellentpickling inhibitors. Some of them are soluble in the dilute acidpickling solutions. Others are insoluble and need to be emulsified ordispersed in the pickling medium.

As the result of extensive tests we have found that the compoundsrepresented by No. 3 above, have considerable value as picklinginhibitors even without further treatment and that they may be used toadvantage in the art of pickling metal. However, we have also discoveredthat the compounds represented by No. 3 above can be "converted bycertain treatments to be described below so as to yield inhibitingmaterials which have a markedly greater value for this purpose than dothe pure compounds represented by structural formula No. 3 above given.Their conversion may be accomplished by:

a. Heating b. By treating with a solution of an alkali, preferably hot.

In the former case (a) the inhibitor is formed directly while in thelatter case (b) the inhibitor usually forms as a phase separate from theaqueous layer, which phase 65 may be separated by any convenient meanssuch as a separatory funnel. However, if the inhibitor does not separateproperly, extraction may be made with a waterimmiscible solvent such aschloroform. After extraction, of course, the inhibitor may be obtainedsimply by evaporation of the solvent.

We also wish to point out that it is not always necessary to use thepure compounds of Formula No. 3 above as a starting point for thepreparation of the inhibitors because it is perfectly feasible to beginwith a reaction mixture containing the materials represented by FormulaNo. 3. For example, as was indicated above, compounds of Formula No. 3can be prepared by the reaction of a ketone, formaldehyde and an aminehydrochloride. The term amine hydrochloride as used in this connectionis to be understood to include ammonium chloride, which readily entersinto this reaction. After proper refluxing, the mixture is made alkalineand the basic material, containing compounds represented by Formula No.3, may be extracted by means of a water immiscible solvent such aschloroform. The solvent may then be evaporated and the residue subjectedto the action of heat or boiled with an alkaline solution. The finalproduct, freed from aqueous liquid, constitutes the inhibitor. It hasbeen found that other amine salts, such as nitrates, acetates, sulfates,etc., may be used in the preparation of the compounds of Formula No. 3.

If the solvent extraction just mentioned is not employed, after thereaction product is made alkaline (preferably by means of a strongalkali such as sodium hydroxide. potassium hydroxide, etc.) the mixtureis heated, preferably boiled, for a period which may vary betweenseveral minutes and several hours. The final product, again freed fromthe aqueous layer, is the inhibitor.

In the above disclosure where we mention the use of heat for theconversion of the substituted piperidines of No. 3. We intend heating toa temperature of from 60 C. to 150 C. and a period of time varying fromfive minutes to twenty-four hours.

As already pointed out, the pure compounds of Formula No. 3 can be usedto good advantage as pickling inhibitors and they may be used either asthe crystalline compounds or as crude bases separated from the reactionmixture by means of a cold alkali treatment. Further, the pure compoundsof the generic formula of No. 3 may be employed as the startingmaterials from which improved inhibitors may be prepared by means ofheat treatment alone or by means of heat treatment, preferably boiling,in the presence of an alkali. Still further, as indicated above, inpreparing our improved inhibitors we may apply the heat and/or alkalitreatment to the reaction mixture used in preparing the compounds of thegeneric Formula No. 3. In other words, a mixture of a ketone, an aminehydrochloride and formaldehyde may be reacted and the reaction mixturetreated with heat and/or an alkali and we prefer relatively long boilingwith an alkali.

We will now give the following examples of ways in which our improvedinhibiting materials may be prepared but before We do so we wish tointroduce the following Table 1 which shows how the materials that wereemployed in the preparation of the inhibitors listed in Table 2 belowfit into the generalized structural Formula No. 3 above:

The following are the examples which we wish to introduce:

iii)

Example A One mole of ammonium chloride, 5 mols. of acetone, and 3 mols.of aqueous formaldehyde solution (37% by weight), are mixed in a literround-bottom flask equipped with condenser. The flask is heated gently,with refluxing, for 15 hours. At the end of this time 2.0 mols. ofacetone are distilled off. The reaction mixture is cooled to 20 C., anda cool (20) solution of 1.25 mols. of NaOH in ml. water is added. Thetemperature of the reaction mixture is maintained at or below 20 C.After 15 minutes the base is shaken out with chloroform. The chloroformsolution is evaporated to dryness in the air (not heat applied), and thebrown resinous base material is dried 2 hours at 50 C. This resinousmaterial, g., is inhibitor A of Table 2. (See below.)

Example B One mole of ammonium chloride, 5 mols. of acetone, and 3 mols.of aqueous formaldehyde solution (37% by weight), are mixed in a literround-bottom flask equipped with condenser. The flask is heated gently,with refluxing, for 15 hours. At the end of this time 2.0 mols. ofacetone are distilled oil. The reaction mixture is cooled to 40 C., anda solution of 1.25 mols. of NaOH in 100 ml. of water is added. Themixture is heated to boiling, with stirring, and is maintained underthese conditions for four hours. At the end of this time the reactionmixture is poured into a separatory funnel. The waste liquor separateson the bottom and is removed. The viscous upper layer is washed withhot, concentrated, sodium chloride solution. After the washing, theblack, viscous layer weighed grams. This material is inhibitor B ofTable 2. (See below.)

Example C One mole of ammonium chloride, 3.0 mols. of methyl ethylketone, and 3 mols. of aqueous formaldehyde (37% by weight) are mixed ina liter round-bottom flask equipped with reflux condenser. The flask isheated gently, with refluxing, for 15 hours. At the end of this time thereaction mixture is cooled to 20 C. and treated with a cool solution of1.25 mols. of NaOH in 100 ml. water. The mixture is heated to boiling,with stirring, and is maintained under these conditions for four hours.The whole reaction mixture is transferred to a separatory funnel, andthe lower aqueous layer removed. The upper layer is washed with hot,saturated sodium chloride solution. The upper layer is now heated on awater bath for 8 hours to remove any excess methyl ethyl ketone. Theresinous mass obtained, weighing 176 grams, is inhibitor C of Table 2.(See below.)

Example D One mole of cyclohexylamine hydrochloride, 4.0 mols. ofacetone, and 2.0 mols. of aqueous formaldehyde (37% by weight), aremixed in a liter round-bottom flask equipped with condenser. The flaskis heated gently, with refluxing for 15 hours. At the end of this time,2.0 mols. of acetone are distilled oil. The reaction mixture is cooledto 20 C., and a cool solution of 1.25 mols. NaOH in 100 ml. water isadded. The reaction mixture is now heated to boiling, with stirring, forfour hours. After this boiling operation has been completed, the wholereaction mixture is transferred to a separatory funnel, and the resinousmaterial separated from the lower aqueous layer. The resinous materialis used without any washing, and weighs 178 g. This is inhibitor D ofTable 2. (See below.)

Example E 30 g. of l-methyl, 4-hydroxy, 4-phenyl, 5 benzoyl piperidine,are boiled over night with a solution of g. of NaOH in 200 ml. water.The product is 25 g. of a brown resinous material, and is inhibitor E ofTable 2. (See below.)

Example F 0.5 mol. ammonium chloride, 1.0 mol. benzalacetone, and 1.0mol. aqueous formaldehyde are mixed in a reaction flask, and refluxedfor hours. The cool reaction mixture is treated with a solution of 30 g.of NaOH in 50 ml. water, and the mixture boiled for 3 hours. Aftersettling in a separatory funnel, the upper layer of inhibitor isseparated from the lower aqueous layer. The inhibitor, 85 g., isinhibitor F of Table 2. (See below.)

Example G This is pure l-n-butyl, 3 benzoyl, 4-hydroxy, 4-phenylpiperidine, prepared according to Plati, Schmidt, and Wenner. This isinhibitor G of Table 2. (See below.)

Example H This is pure l-benzyl, 3-benzoyl, 4-hydroxy, 4-phenylpiperdine, prepared according to Plati, Schmidt, and Wenner. This isinhibitor H of Table 2. (See below.)

Example I Example I 3.0 mols. of acetone, 3.0 mole. of aqueousformaldehyde solution (37%), and 1.0 mol. of NHtCl were reacted underreflux over night. The solution was cooled, and 100 ml. of reagent gradeNH4OH solution added. The solution was stirred and heated (75 C.) for 4hours. At the end of this time, the solution was cooled, and 300 ml. ofchloroform added, with shaking. The chloroform was separated, and anadditional 200 ml. of chloroform added, with shaking. The totalseparated chloroform was evaporated on a water bath. The total residue,110 g., is inhibitor J of Table 2. (See below.)

That there is a profound change in the chemical structure of the4-hydroxy piperidine of Figure 3 on treatment with alkalies or byheating without alkalies, in accordance with any one of the foregoingexamples, is evidenced by important changes in physical properties, suchas appearance, solubility, infra-red absorption spectrum, etc. Theinhibitors which are formed are highly complex compounds characterizedby the presence of carbon, oxygen, hydrogen and nitrogen; they are basescapable of reacting with mineral acids to form salts; they are solublein methyl alcohol or chloroform and are substantially insoluble in watercontaining sodium hydroxide while having considerable solubility inwater acidulated with hydrochloric acid.

The inhibitors of the various examples given above were tested andevaluated according to the following table:

TABLE NO. 2

Inhibition, Inhibitor Starting measured specimen materla Method ofpreparation of inhibitor as lfitln We 8 gJItJ/hr.

A V Crude base separated from reaction 8. 6

mixture by means of cold alkali and 01101;. B V Crude base separatedfrom reaction 1.9

. mixture by means of boiling alkali (4 hours). 0 I 3. 7 D II do 2. 5 EIII Pure material boiled with NaOH 1. 0

solution 4 hours, then separated. F IV Orude bass separated fromreaction 2. 2

mixture by means of boiling alkali (3 hours). G VI Platl, Schmidt andWanner, J. Org. 42. 8

Chem, 14, 873-878 (1949). H VII 12. 6 I V Base separated by means ofNaOH 2. 4

solution, 5 minutes, at 0. Then heated 8 hours at C. in absence of NaOH..1 V NHAOH solution added to reaction 6. 7

mixture; heated to 75 0., 4 hrs. Product extracted with chlororm. BlnnkNo inhibitor 105.6

The inhibitor test used to evaluate the inhibitors referred to in TableNo. 2, just above, is as follows: 0.05 gram of the compound or mixtureare dissolved or suspended in a mixture of 20 milliliters 66 B. sulfuricacid, 1 milliliter C. P. (23 B.) hydrochloric acid and milliliterswater. The solution was heated to 180 F. and aged for two hours. Afterthe ageing, a weighed test strip of hot rolled steel, previously pickledin 1:1 hydrochloric acid solution at room temperature for 10 minutes,was immersed in the test solution for 30 minutes, the temperature of thetest solution being maintained at 180 F. The strip was then removed fromthe test solution, rinsed in water, alcohol dried and weighed. The lossin weight expressed as grams/sq. ft./hour was reported as noted in thetable above. The blank was run in a similar fashion except that noinhibiting material or compound was added to the test solution.

The inhibitors which We have described lend themselves exceptionallywell to inhibitor formulations. As is well known in this art, quiteoften it is desirable (in order to formulate inhibitor compounds of thehighest possible value and greatest utility for present day commercialpractice) to use the primary inhibitor or principal inhibitor with othermaterials which, for the sake of brevity, will be called hereinadjuncts." For instance, some inhibitor formulations may be made byincorporating therein wetting agents, bone tar oil, high boiling coaltar bases, both cyclic and heterocyclic, foam producing materials, etc.Additionally, the most important inhibitor formulations of the presentinvention are those embodying the primary reaction product in admixturewith sulfur-bearing compounds such as thiocyanates and thioureas,including both alkyl or aryl substituted thioureas. Especially goodresults are usually obtained when the admixtures are heated. Specificexamples of such inhibitor formulations are as follows:

FORMULATION 1 Sulfuric acid 66 B -.ml.. 49.8

In a separate container the sulfuric acid and the water are mixed andcooled to 40 C. The reaction product of Example B is dissolved in thisacid mixture and the solution cooled to 30 C. The muriatic acid is thenadded and the solution heated to 80 C. At this point the thiourea isadded and the solution heated to 100 C. This temperature is maintainedfor one hour. At the end of the hours heating, the admixture is allowedto cool. The cooled admixture is an extremely strong longlastinginhibitor formulation.

The inhibitors of the present invention are primarily useful in the artof pickling and cleaning metal especially where the acids employedconsist of dilute solutions of non-oxidizing mineral acids such assulphuric, hydrochloric and phosphoric acids as well as solutions ofacid salts such as acid sulphate and the like. The typical example isthe pickling of iron and steel articles such as sheets, forgings, bars,wire and other articles at various stages of their manufacture.Naturally the composition of these pickling or metal treating solutions,their temperature of use and other factors vary with differentoperations but in every instance the primary function of the solution isto remove undesirable incrustations from the metal while at the sametime restraining the attack of the acids upon the exposed metal andthereby to conserve both acid and metal and to prevent or minimizedamage such as hydrogen embrittlement, burning, or overpickling. Thequantity of the inhibitor to be used, naturally, will vary dependingupon any given set of conditions but those skilled in the art ofpickling can easily determine the proportions to be employed. Theinvention is entirely independent of quantities except, of course, thata sufficient quantity should be employed to produce a useful result andin this connection, because of the improved character of our newinhibitors, it is frequently possible to reduce the quantity ofinhibitor which may be required for any particular operation.

We claim:

1. An acid corrosive to metals containing, as an inhibiting agent, thereaction product formed by heating at temperatures of from 60 C. to 150C. for a period of time of from five minutes to twenty-four hours asubstituted 4hydroxy piperidine having the general formula:

wherein R is from the class consisting of alkyl and cycloalkyl radicalscontaining no more than eight carbon atoms, aryl-alkyl radicals in whichthe aryl moiety contains no more than eleven carbon atoms, hydrogen, and

0H CH:

ll CHr-C-C 2 /CH: N

at temperatures of from C. to C. for a period of time of from fiveminutes to twenty-four hours, the said reaction product being present inthe acid in an amount sufficient to materially retard the attack of theacid on basis metal.

References Cited in the file of this patent UNITED STATES PATENTS2,010,562 Parkes Aug. 6, 1935 2,499,283 Robinson Feb. 28, 1950 2,604,451Rocchini July 22, 1952 2,630,368 Wachter et al. Mar. 3, 1953 OTHERREFERENCES Beilstein: Handbook of Organic Chemistry (Springer), 2d. sup.vol. 21, page 412.

Plati et al.: Journal of Organic Chemistry, vol. 14, pages 543-549(1949).

Plati et al.: Journal of Organic Chemistry, vol. 14, pages 873-878(1949).

Blicke et al.: Journal of the American Chemical Society, vol. 64, pages451-454.

Mannich et al.: Arcbiv der Pharmazie, vol. 1926, page 66.

1. AN ACID CORROSIVE TO METALS CONTAINING, AS AN INHIBITING AGENT, THE REACTION PRODUCT FORMED BY HEATING AT TEMPERATURES OF FROM 60*C. TO 150*C. FOR A PERIOD OF TIME OF FROM FIVE MINUTES TO TWENTY-FOUR HOURS A SUBSTITUTED 4-HYDROXY PIPERIDINE HAVING THE GENERAL FORMULA: 